This site is being deprecated.
Please see the official X‑Plane Support page for help.
It sounds like your joystick preferences got messed up somehow. If you find the exact steps to recreate the update messing up your preferences, please file a bug report.
Otherwise, I think you should be able to go into the Joystick and Equipment screen and reprogram the button to be trim pitch up again.
This site is no longer being actively maintained.